I would go with the gills and a few bass. Those species will do Ok with the warmer water. If you put in pike that's all that will be there. Like OT said the brookies if they are in the parent stream will go to the dam and get big. With a beaver dam I would be more interested in how big it can get. Sooner or later they can get unmanageable and take over the land if you allow that. Mother nature can also remove the dam with high water which if the dam is large enough can be bad down stream. I have seen whole roads washed out from a large dam that breached with a large rainstorm dumping several inches in a short time. Good luck with the dam though..it can be a great place to watch wildlife.